Latent heat exchanger and water heater

ABSTRACT

A latent heat exchanger ( 1 ) has a casing ( 2 ), a heat-absorbing tube ( 50 ) accommodated in the casing ( 2 ), an inlet header ( 60 ), and an outlet header ( 70 ). The casing ( 2 ) has a casing main body ( 10 ) and a top plate ( 40 ) closing an upper opening ( 16 ) of the casing main body ( 10 ). The back wall ( 11 ), the front wall ( 12 ), the bottom wall ( 13 ), one side wall ( 14 ), and the other side wall ( 15 ) of the casing main body ( 10 ) are formed integrally by draw-processing a single metal plate.

FIELD OF THE INVENTION

The present invention relates to a latent heat exchanger for recoveringlatent heat by condensing water vapor in combustion gas and a waterheater comprising the latent heat exchanger.

BACKGROUND ART

Conventionally, there has been known a so-called condensing type waterheater having a sensible heat exchanger and a latent heat exchanger inan apparatus body. In this kind of the water heater, after sensible heatin combustion gas is absorbed by the sensible heat exchanger, latentheat in the combustion gas is absorbed by the latent heat exchanger. Asthe latent heat exchanger, there has been proposed one disclosed in,e.g., Patent Document 1 or Patent Document 2, for miniaturization andhigher heat efficiency. As shown in FIGS. 13 and 15, in such a latentheat exchanger, a plurality of heat absorbing pipes 820 or a pluralityof heat absorbing pipes 920 each having a pipe structure in which astraight portion and a circularly arcuate turn-around portion arerepeated consecutively, are arranged in a meandering or spiral manner,in a casing where combustion gas flows, and in order to circulate fluidto be heated in the heat absorbing pipes 820 or the heat absorbing pipes920, upstream ends and downstream ends of the heat absorbing pipes 820or 920 are connected respectively to an inlet header 830 or 930 and anoutlet header 840 or 940 in one side wall 814 or 914 of the casing.

When the latent heat in the combustion gas is absorbed by the latentheat exchanger as described above, strong acidic drain (condensed water)is generated in the casing by cooling water vapor in the combustion gasbelow the dew point temperature and condensing the water vapor. Thus, inorder to prevent corrosion due to the drain, a member made ofanti-corrosive metal such as stainless steel or titanium has been usedas the casing and the heat absorbing pipe. Further, in order to quicklydischarge the drain from the casing inside, a drain discharge opening isformed in a lower area of the casing.

As shown in FIG. 14, in assembling the latent heat exchanger of thePatent Document 1 described above, an upper casing 812 having upperprojecting portions 812 a projecting downward respectively from fourcorners thereof and a lower casing 813 having lower projecting portions813 a projecting upward respectively from four corners thereof arewelded such that the upper and lower projecting portions 812 a, 813 aabut each other, whereby a tubular casing body 811 having both-sideopenings is produced. Subsequently, as shown in FIG. 13, peripheries ofthe both-side openings of the casing body 811 are welded respectively toan one side wall 814 to which the upstream and downstream ends of theheat absorbing pipes 820 are brazed and the other side wall 815.Similarly, as shown in FIG. 16, a casing of the latent heat exchanger ofthe Patent Document 2 is produced by brazing a top member 915, a pair ofside walls 913, 914, and a main body member 911 having a concavecross-section and serving as a front wall 911 a, a back wall 911 b, anda bottom wall 911 c.

In the latent heat exchanger having the above casing, when strong aciddrain dripped from the heat absorbing pipes during an operation proceedsto the lower corners of the casing, the drain easily enters a gapexisting in a welded or brazed connection area between the peripheriesof the both-side openings of the casing body or the main body member andthe side walls, which may result in long-term retention of the strongacid drain in the gap. Further, when metal plates are connected to eachother by welding, the metal plates are potentially transformed at thewelded area. As such, even if the metal plates inherently excellent inanti-corrosion are used, the anti-corrosion ability partially isdeteriorated at the welded area. Thus, there is a problem that the metalplates become easily corroded at both lower sides of the casing wherethe drain is likely to be retained. Further, in the latent heatexchanger manufactured by connecting many metal plates by welding orbrazing, there are problems that a number of members increase and anassembling work becomes complicated due to increase of members to beconnected.

[Prior Arts]

-   [Patent Document 1] JP2009-180398 A-   [Patent Document 2] JP2008-292032 A

SUMMARY OF THE INVENTION

The present invention has been made to solve the problems describedabove, and an object of the present invention is to provide a latentheat exchanger, for which miniaturization and higher heat efficiency arerequired, capable of reducing corrosion due to the drain so as toenhance durability and being produced in a simple process, and a waterheater using the latent heat exchanger.

According to one aspect of the present invention, there is provided alatent heat exchanger comprising:

a casing having a flow path of combustion gas therein;

a heat absorbing pipe accommodated in the casing;

an inlet header for introducing fluid to be heated into the heatabsorbing pipe; and

an outlet header for discharging the fluid to be heated from the heatabsorbing pipe, wherein

the casing has a box-shaped casing body having an upper opening and atop board closing the upper opening of the casing body,

the casing body has a back wall, a front wall, a bottom wall having adrain discharging opening, one side wall having an upstreamend-inserting hole through which an upstream end of the heat absorbingpipe is inserted and a downstream end-inserting hole through which adownstream end of the heat absorbing pipe is inserted, and the otherside wall,

the back wall, the front wall, the bottom wall, the one side wall, andthe other side wall are integrally formed by drawing one single metalplate, and

the inlet header and the outlet header are respectively disposed outsidethe one side wall and connected to the upstream and downstream ends ofthe heat absorbing pipe led outside the one side wall through theupstream end-inserting hole and the downstream end-inserting hole.

According to the present invention, since no connection area by weldingor brazing is formed in a lower area of the casing of the latent heatexchanger, drain is not likely to be retained in the lower area of thecasing. Therefore, it makes possible to smoothly discharge the drainfrom the drain discharge opening provided at the lower area of thecasing. As a result, corrosion of the metal plates due to the drain canbe reduced, whereby it makes possible to provide the latent heatexchanger and the water heater excellent in durability. Further, sincethe casing is formed by closing the upper opening of the casing body,whose walls are integrally formed by the drawing, with the top board, itmakes possible to manufacture the latent heat exchanger easily withfewer members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view showing one example of a latentheat exchanger according to an embodiment 1 of the present invention;

FIG. 2 is a schematic exploded perspective view of FIG. 1;

FIG. 3 is a partial schematic cross-sectional view showing an internalstructure on the other side wall side of the latent heat exchangeraccording to the embodiment 1 of the present invention;

FIG. 4 is a schematic perspective view showing a side baffle plateaccording to the embodiment 1 of the present invention;

FIG. 5 is a schematic perspective view showing a heat absorbing pipeaccording to the embodiment 1 of the present invention;

FIG. 6 is a schematic cross-sectional view showing a circularly arcuateturn-around portion of the heat absorbing pipe according to theembodiment 1 of the present invention;

FIG. 7 is a schematic cross-sectional view showing a straight portion ofthe heat absorbing pipe according to the embodiment 1 of the presentinvention;

FIG. 8 is a schematic cross-sectional view as taken along A-A of FIG. 1;

FIG. 9 is a partial schematic cross-sectional view showing a connectionstep for connecting a casing body and a top board by a fastening processaccording to the embodiment 1 of the present invention, wherein FIG. 9Ashows a state before connection and FIG. 9B shows a state afterconnection;

FIG. 10 is a schematic block diagram showing one example of a waterheater according to the embodiment 1 of the present invention;

FIG. 11 is a schematic perspective view showing one example of a latentheat exchanger according to an embodiment 2 of the present invention;

FIG. 12 is a schematic block diagram showing one example of a waterheater according to the embodiment 2 of the present invention;

FIG. 13 is a schematic perspective view showing one example of aconventional latent heat exchanger;

FIG. 14 is a schematic perspective view showing a casing body of FIG.13;

FIG. 15 is a schematic perspective view showing another example of aconventional latent heat exchanger; and

FIG. 16 is a schematic perspective view showing a casing of FIG. 15.

PREFERRED MODE FOR CARRYING OUT THE INVENTION Embodiment 1

Hereinafter, a latent heat exchanger and a water heater having thelatent heat exchanger according to an embodiment of the presentinvention will be described in detail.

FIG. 1 is a schematic perspective view showing one example of the latentheat exchanger according to the embodiment 1 of the present invention,and FIG. 2 is a schematic exploded perspective view of FIG. 1.

As shown in FIGS. 1 and 2, a casing 2 of the latent heat exchanger ofthe embodiment has a box-shaped casing body 10 having an upper opening16 and a top board 40 closing the upper opening 16 of the casing body10. Those casing body 10 and top board 40 are respectively formed fromone thin plate made of a metal having anti-corrosion such as stainlesssteel.

A casing body 10 has a back wall 11, a front wall 12, a bottom wall 13,one side wall 14, and the other side wall 15. The casing body 10 isintegrally formed in a box shape and has the upper opening 16, bydrawing one single metal plate. More in detail, the back and front walls11, 12 rise from front and back edges of the plate shaped bottom wall 13extending in a predetermined direction, and those walls 11 and 12 areintegrally connected to the bottom wall 13 via corners. Also, the oneand other side walls 14, 15 rise from right and left edges of the bottomwall 13, and those side walls 14, 15 are integrally connected to thebottom wall 13 via corners. Further, right and left edges of each of theback and front walls 11, 12 are connected integrally to the one andother side walls 14, 15, respectively, via corners. With thisconfiguration, an internal space having the upper opening 16, that issurrounded by the back wall 11, the front wall 12, the bottom wall 13,and the both side walls 14, 15, is formed in the casing body 10. In thepresent embodiment, a mounting portion 101 for mounting thereon a topboard 40 when the casing body 10 and the top board 40 are connected toeach other by a fastening process, that is bent the respective walls 11,12, 14, 15 in the horizontal direction, and an upper flange portion 102for fastening the top board 40 therein by the fastening process (to bedescribed later), that is bent upwardly from the mounting portion 101,are consecutively formed at opening ends of the back wall 11, the frontwall 12, and the both side walls 14, 15.

Accordingly, when the casing body 10 according to the embodiment ismanufactured, there is no need of welding or brazing. Further, since noconnection area by welding or brazing is formed at a lower area of thecasing 2 having the casing body 10, the drain is not likely to beretained in the lower area when the drain is generated. Furthermore,since the back wall 11, the front wall 12, the bottom wall 13, and theone and other side walls 14, 15 are integrally formed by the drawing,the casing 2 can be easily formed with fewer members.

A combustion gas inlet port 111 for introducing the combustion gas intothe casing and a combustion gas outlet port 121 for discharging thecombustion gas out of the casing, that are opened in a laterally longrectangular shape, are respectively formed at substantially center areasin both up-down and left-right directions of the back wall 11 and thefront wall 12, when a latent heat exchanger 1 is assembled in anapparatus body of a water heater. With this configuration, a flow pathof the combustion gas communicating from the combustion gas inlet port111 to the combustion gas outlet port 121 is formed inside the casing 2.A shape and an opened position of the combustion gas inlet port 111 orthe combustion gas outlet port 121 can be appropriately set according tothe form of use. For example, according to the form of the water heater,the combustion gas inlet port 111 may be formed at the bottom wall 13 orthe combustion gas outlet port 121 may be formed at the top board 40.

The bottom wall 13 is inclined downward from a back wall 11 side to afront wall 12 side in order to smoothly discharge the drain out of thecasing 2 upon a generation of the drain, and a drain discharge opening17 for discharging the drain is opened in the lowest area of theinclined plane. The drain discharge opening 17 is connected to aneutralizer via a discharge pipe (not shown). Lower protrusions 131, 131are formed in the bottom wall 13 by the drawing so as to protrudeinwardly into the casing 2 from both ends (one side wall 14 side end andthe other side wall 15 side end) in the left-right direction, in a statewhere the casing body 10 and the top board 40 are connected to eachother. The lower protrusions 131, 131 are respectively formed at alocation abutting circularly arcuate turn-around portions 52 of abottommost heat absorbing pipe 50.

A plurality of upstream end-inserting holes 141 through which upstreamends 53 of the heat absorbing pipes 50 are inserted and a plurality ofdownstream end-inserting holes 142 through which downstream ends 54 ofthe heat absorbing pipes 50 are inserted are formed, by burring, in bothends (the back wall 11 side end and the front wall 12 side end) of theone side wall 14 in the front-back direction, as many as the heatabsorbing pipes 50. In the present embodiment, the upstreamend-inserting holes 141 and the downstream end-inserting holes 142 arerespectively arranged in two rows, which are staggered with respect toeach other. The number and arrangement of the inserting holes 141, 142can appropriately be selected in accordance with the number of the heatabsorbing pipes 50. The other side wall 15 is same as the one side wall14 except that the upstream end-inserting holes 141 and the downstreamend-inserting holes 142 are not formed.

The top board 40 has a top board body 41 in a flat plate shape, astanding strip 42 formed by bending upward an entire periphery of thetop board body 41, and a lower flange portion 43 formed by bending backan entire periphery of the standing strip 42 in a horizontal direction.The top board 40 is formed by drawing one single metal plate, same asthe casing body 10. The standing strip 42 is sized so as to fit withinan inner periphery of the upper opening 16, which is surrounded by theback wall 11, the front wall 12, the one and other side walls 14, 15 ofthe casing body 10. Further, the lower flange 43 is sized so as to bemounted on the mounting portion 101. Furthermore, upper protrusions 144,144 are formed in the top board body 41 by the drawing so as to protrudeinwardly into the casing 2 from both ends (the one side wall 14 side endand the other side wall 15 side end) in the left-right direction, in astate where the casing body 10 and the top board 40 are connected toeach other. The upper protrusions 144, 144 are respectively formed at alocation abutting circularly arcuate turn-around portions 52 of anuppermost heat absorbing pipe 50 as described later.

As shown in FIGS. 3 and 4, an upper end of a side baffle plate 45 in aflat plate shape is welded to a lower surface of the top board 40 on theother side wall 15 side. The side baffle plate 45 is arranged in thecasing 2 such that a plate portion 451 extends along a flow pathdirection of the combustion gas in a state where the casing body 10 andthe top board 40 is connected to each other. That is, the casing body 10integrally formed by the drawing is used in the latent heat exchanger 1according to the present embodiment, so that it is necessary to lead outthe upstream and downstream ends 53, 54 of the heat absorbing pipes 50through the one side wall 14 in connecting the upstream and downstreamends 53, 54 of the heat absorbing pipes 50 respectively to an inletheader 60 and an outlet header 70 disposed outside the one side wall 14.Thus, when the upstream and downstream ends 53, 54 of the heat absorbingpipes 50 are inserted through the upstream end-inserting holes 141 andthe downstream end-inserting holes 142, respectively, there occurs aspace having a certain volume between ends of the circularly arcuateturn-around portions 52 on the other side wall 15 side and an innersurface of the other side wall 15. This causes the combustion gasintroduced through the combustion gas inlet port 111 to flow in thespace with less gas glow resistance, which may result in preventing thecombustion gas from efficiently contacting the heat absorbing pipes 50and reducing in heat efficiency. However, providing the side baffleplate 45 in the space between the ends of the circularly arcuateturn-around portions 52 on the other side wall 15 side and the innersurface of the other side wall 15 causes the combustion gas to flowtoward the heat absorbing pipes 50 side, making it easy for thecombustion gas to contact the heat absorbing pipes 50, thereby allowingenhancement of the heat efficiency. In addition, since the upper end ofthe side baffle plate 45 is connected to the lower surface of the topboard 40, the casing 2 can be fabricated simply by closing the upperopening 16 of the casing body 10 with the top board 40 to which the sidebaffle plate 45 has been connected.

Further, as shown in FIG. 4, the side baffle plate 45 according to thepresent embodiment is formed of a flat plate portion 451 having, at anupper end thereof, a connection portion 450 for connecting to the lowersurface of the top board 40 and inclined faces 452, 452 respectivelyinclined in a manner curved, from ends on a combustion gas inlet port111 side and a combustion gas outlet port 121 side toward the heatabsorbing pipes 50. With this configuration, since the combustion gasintroduced into the casing 2 from the combustion gas inlet port 111flows along the inclined faces 452, 452 on the combustion gas inlet port111 side and the combustion gas outlet port 121 side, it makes easierfor the combustion gas to contact the heat absorbing pipes 50, therebyallowing further enhancement of the heat efficiency. Alternatively, theinclined faces 452, 452 may be linearly inclined.

Further, as shown in FIG. 3, the side baffle plate 45 is formed suchthat a lower end thereof does not abut an inner surface of the bottomwall 13. If the side baffle plate 45 extends to such an extent that thelower end thereof abuts the bottom wall 13, vibration of the side baffleplate 45 is transmitted both to the top board 40 and the bottom wall 13when the combustion gas passes inside the casing 2, resulting in easygeneration of noise. However, the side baffle plate 45 only abuts thelower surface of the top board 40 but not the bottom wall 13, so thatsuch noise can be prevented. Further, flow of drain is not disturbed, sothat it makes possible to discharge the drain smoothly. Moreover, sinceno connection area is formed between the bottom wall 13 and the sidebaffle plate 45, there is no need to take care of crevice corrosion dueto the drain.

Referring back to FIG. 2, an upper baffle plate 46 is connected to thetop board 40, that is inclined downward from the lower surface of thetop board 40 on the front wall 12 side toward an entire upper edge ofthe opening of the combustion gas outlet port 121. With thisconfiguration, the combustion gas introduced from the combustion gasinlet port 111 is further suppressed from an upper side to the heatabsorbing pipe 50 side, it makes easy for the combustion gas to contactthe heat absorbing pipes 50 and to smoothly discharge out of the casing2 from the combustion gas outlet port 121 along the upper baffle plate46 on the combustion gas outlet port 121 side.

Inside the casing 2, a plurality of (five, in the present embodiment)heat absorbing pipes 50 through which tap water serving as fluid to beheated flows are accommodated in a meandering manner with a gap allowingpassage of the combustion gas provided between one another. The upstreamand downstream ends of the heat absorbing pipes 50 are respectively ledoutside the one side wall 14 through the upstream end-inserting hole 141and the downstream end-inserting hole 142 formed in the one side wall14, as described above.

FIG. 5 is a schematic perspective view showing one of the heat absorbingpipes 50. The heat absorbing pipe 50 according to the present embodimentis formed by bending a plurality of portions of a corrugate pipe (pipehaving an outer shape in which ridge portions and valley portionscontinuously alternate in an axial direction thereof) made of ananti-corrosion metal such as stainless steel. Further, the heatabsorbing pipe 50 has a pipe structure in which a straight portion 51and the circularly arcuate turn-around portion 52 are repeatedconsecutively and has a wave shape in which the straight portions 51 andthe circularly arcuate turn-around portions 52 are made to meander inone plane. (In FIGS. 1, 2 and so on, a part of the straight portion 51is only described as the corrugate pipe for avoiding complication.) Eachof the heat absorbing pipes 50 is accommodated in the casing 2 such thatthe straight portion 51 extends in the left-right direction between theone and other side walls 14, 15 and the circularly arcuate turn-aroundportions 52 are disposed at both ends (the one side wall 14 side end andthe other side wall 15 side end) in the left-right direction. Aplurality of the heat absorbing pipes 50 formed by connecting thestraight portion 51 to the circularly arcuate turn-around portions 52bent at one direction may be used and such heat absorbing pipes 50 maybe accommodated in a spiral manner in the casing 2.

As shown in FIGS. 5 and 6, the circularly arcuate turn-around portions52 of the heat absorbing pipes 50 each have a cross section flattened ina direction that the heat absorbing pipes 50 are stacked one another.FIG. 6 shows a cut shape of the valley portion of the heat absorbingpipe 50. On the other hand, as shown in FIG. 7, the valley portion ofthe straight portion 51 of the heat absorbing pipe 50 has a circularcross section.

As shown in FIGS. 2 and 3, the heat absorbing pipes 50 each are stackedat the flattened circularly arcuate turn-around portions 52. With thisconfiguration, a gap between the heat absorbing pipes 50 adjacent toeach other is narrowed in the stacking direction of the heat absorbingpipes 50, whereby the heat absorbing pipes 50 are arranged densely. As aresult, it makes possible to downsize the latent heat exchanger 1 and tobring into contact the combustion gas with the heat absorbing pipes 50efficiently.

The heat absorbing pipes 50 stacked one another are displaced byhalf-pitch in a wavelength direction of the wave shape. That is, in FIG.2, with respect to a second heat absorbing pipe 50 from the top and asecond heat absorbing pipe 50 from the bottom, their adjacent heatabsorbing pipes 50 are provided at positions displaced by half-pitch inan upstream side of the flow path of the combustion gas (to thecombustion gas inlet port 111 side).

The flattened circularly arcuate turn-around portions 52 of theuppermost heat absorbing pipe 50 and the bottommost heat absorbing pipe50, which are positioned at the both ends (both ends on the one sidewall 14 side and the other wall 15 side) in the left-right direction,abut the above-described upper protrusions 144 formed in the top board40 and the lower protrusions 131 formed in the bottom wall 13,respectively. With this configuration, without using other member forfixing the heat absorbing pipes 50, the heat absorbing pipes 50 can befixed stably in the casing 2. Also, vibration of the heat absorbingpipes 50 due to water hammer phenomenon or the like can be reduced.Further, since other member for fixing the heat absorbing pipes 50 isnot arranged in the flow path of the combustion gas except for the heatabsorbing pipes 50, it makes possible to bring into contact thecombustion gas with the heat absorbing pipes 50 efficiently.

As described above, the upstream and downstream ends 53, 54 of the heatabsorbing pipes 50 are respectively led outside the casing 2 through theupstream end-inserting holes 141 and the downstream end-inserting holes142 formed in the one side wall 14. Further, as shown in FIG. 1, theupstream and downstream ends 53, 54 are respectively connected to theinlet header 60 and the outlet header 70 disposed outside the one sidewall 14. As such, the upstream and downstream ends 53, 54 of the heatabsorbing pipes 50 are connected to the inlet and outlet headers 60, 70,respectively and thus, as a whole, the plurality of heat absorbing pipes50 are connected in parallel. This reduces a water-passing resistance ascompared to a case where the heat absorbing pipes 50 are connected inseries.

The inlet and outlet headers 60, 70 which are respectively connected tothe upstream and downstream ends 53, 54 of the heat absorbing pipes 50are arranged outside the one side wall 14 of the casing body 10. Asshown FIGS. 1 to 2 and further FIG. 8 showing a cross-sectional view astaken along A-A of FIG. 1, the both headers 60, 70 respectively haveheader main bodies 61, 71 in a dish shape and header covers 64, 74 in adish shape to be internally fitted respectively to the header mainbodies 61, 71. The both headers 60, 70 are formed respectively byconnecting their members by brazing such that openings of the headermain bodies 61, 71 and those of the header covers 64, 74 face eachother. The outlet header 70 according to the present embodiment has thesame configuration as that of the inlet header 60 except for using theheader cover 74 obtained by turning upside down the header cover 64 ofthe inlet header 60. Thus, a description will be given mainly of theinlet header 60 below.

As seen well in FIG. 8, the header main body 61 has a main body bottomplate 62 having connection holes 160 to be connected to the upstreamends 53 of the heat absorbing pipes 50 and a main body peripheral wall63 raised from a peripheral end of the main body bottom plate 62 towarda header cover 64 side and opened toward the header cover 64 side, in astate where the header main body 61 and the header cover 64 are fittedto each other. In the embodiment, the both headers 60, 70 are providedadjacent to the one side wall 14. However, the upstream ends 53 or thedownstream ends 54 of the heat absorbing pipes 50 may be furtherextended apart from the casing 2 and the upstream ends 53 or thedownstream ends 54 of the extended heat absorbing pipes 50 may beconnected to the inlet header 60 or the outlet header 70.

The main body peripheral wall 63 of the header main body 61 is made toextend such that at least a part of a main body open end 630 ispositioned higher than an outer peripheral surface of a cover bottomplate 65 in a cross-sectional direction, in a state where the headercover 64 is fitted to the header main body 61. Also, as shown in FIG. 2,the main body peripheral wall 63 of the header main body 61 is formedinto substantially a rectangular shape having a pair of long sides 63 aand a pair of short sides 63 b. Further, as shown in FIG. 8, the mainbody open end 630 of the long and short sides 63 a, 63 b is formed so asto wide outwardly. With this configuration, when the header main body 61and the header cover 64 are brazed to each other, a brazing reservoir Mis formed between an inner surface of the main body peripheral wall 63and an outer surface of a cover peripheral wall 66. As a result, itmakes possible to enlarge a connection area to be brazed between theinner surface of the main body peripheral wall 63 and the outer surfaceof a cover peripheral wall 66. Further, since a brazing material spreadsin the brazing reservoir M, it makes possible to prevent the brazingmaterial from depositing on unnecessary area during the brazing process,as compared to a case where the brazing material is applied only on edgeface of the main body open end 630.

Further, according to the present embodiment, claws 67, 67, which arebent toward the header cover 64 side after the header main body 61 andthe header cover 64 are fitted to each other, are respectively formed inthe main body open end 630 of the opposing long sides 63 a of the headermain body 61. Those claws 67, 67 are arranged such that they are notoverlapped in a short side 63 b direction. Specifically, in theembodiment, since the header main body 61 and the header cover 64fitting into the header main body 61 are brazed, it is necessary topress the header cover 64 into the header main body 61 before thebrazing. However, since the peripheral walls 63, 66 of the header mainbody 61 and the header cover 64 have fabrication errors respectively,there is a possibility that the header cover 64 cants with respect tothe header main body 61 or the header cover 64 removes from the headermain body 61 after pressing-in. From this point of view, the claws 67 tobe bent toward the header cover 64 side are formed in the main body openend 630 of the main body peripheral wall 63. Thus, after the headercover 64 and the header main body 61 are fitted to each other, the claws67 abutting an outer peripheral surface of the header cover 64 suppressbacklash of the header cover 64, thereby reliably preventing shift ofthe header cover 64. Further, forming the claws 67 in the main body openend 630 of the long sides 63 a allows the header cover 64 to be fixed tothe header main body 61 avoiding an inflow port 164 to which a watersupply pipe is connected. The number of the claws 67 may be one, orthree or more in accordance with a size of the header main body 61. In acase where the main body open end 630 of the main body peripheral wall63 has the claw 67, the main body open end 630 preferably is extendedsuch that a part of the main body open end 630 other than a part inwhich the claw 67 is formed, is equal to or higher than the outerperipheral surface of the cover bottom plate 65 in a cross sectionaldirection upon fitting the header cover 64 to the header main body 61.

The header cover 64 connected to the header main body 61 has the coverbottom plate 65 and the cover peripheral wall 66 raised from aperipheral end of the cover bottom plate 65 toward a header main body 61side and opened toward the header main body 61 side, in a state wherethe header main body 61 and the header cover 64 are fitted to eachother. The cover peripheral wall 66 is formed into a substantiallyrectangular shape having a pair of long sides and a pair of short sides,same as the main body peripheral wall 63 of the header main body 61,such that the outer surface of the cover peripheral wall 66 fits intothe inner surface of the main body peripheral wall 63.

As shown in FIG. 2, the inflow port 164 and an outflow port (not shown)are respectively formed near an upper end of the cover bottom plate 65and a lower end of the cover bottom plate 75 by burring. Joint cylinders68, 78 for connecting respectively to the water supply pipe and aconnection pipe connecting to an upstream end of a pipe body of asensible heat exchanger are attached respectively to the inflow port 164and the outflow port. With this configuration, the fluid to be heatedflows from the inlet header 60 to the outlet header 70 via the pluralityof the heat absorbing pipes 50 and water vapor in the combustion gas iscondensed on outer surfaces of the heat absorbing pipes 50, resulting inrecovery of the latent heat.

Next, one example of a manufacturing method of the latent heat exchangeraccording to the embodiment will be described in detail.

In manufacturing the latent heat exchanger 1, firstly, the upstream anddownstream ends 53, 54 of the heat absorbing pipes 50 are respectivelyinserted through the upstream end-inserting holes 141 and the downstreamend-inserting holes 142 of the one side wall 14 of the casing body 10formed by the drawing and the upstream and downstream ends 53, 54 of theheat absorbing pipes 50 are led outside the one side wall 14 by apredetermined length. Then, the brazing material (for example,nickel-based brazing paste) is applied to boundaries between outersurfaces of the led-out heat absorbing pipes 50 and the upstreamends-inserting holes 141 and the downstream ends-inserting holes 142.Subsequently, the upstream and the downstream ends 53, 54 of the led-outheat absorbing pipe 50 are respectively inserted through the connectionholes 160, 170 of the header main bodies 61, 71 and the brazing materialis applied to boundaries between the outer surfaces of the upstream andthe downstream ends 53, 54 and the connection holes 160, 170. Thebrazing material can be pre-applied at inner surfaces of the upstreamend-inserting holes 141 and the downstream end-inserting holes 142 ofthe one side wall 14 and inner surfaces of the connection holes 160, 170of the header main bodies 61, 71.

Alternatively, the joint cylinders 68, 78 are respectively inserted intothe inflow port 164 and the outflow port (not shown) of the headercovers 64, 74 in advance and those are prefixed by applying brazingmaterial to their boundaries. Then, the header covers 64, 74 are placedbetween jig holding portions P, P formed in the main body peripheralwalls 63, 73 of the header main bodies 61, 71 and a pushing jig (notshown) such that the openings of the header covers 64, 74 and those ofthe header main bodies 61, 71 face each other, and the header covers 64,74 are pressed into the header main bodies 61, 71 by the pushing jig.After pressing-in, the claws 67, 77 formed in the main body open ends630, 730 of the main body peripheral walls 63, 73 are respectively benttoward the header covers 64, 74 sides and further the brazing materialis applied into the brazing reservoirs M formed between the innersurfaces of the main body peripheral walls 63, 73 and the outer surfacesof the cover peripheral walls 66, 76. At this time, although the claws67, 77 are respectively bent toward the header covers 64, 74 sides, thebrazing material penetrates into base portions of the claws 67, 77 bypenetrating ability of the brazing material.

Next, as shown in FIG. 9A, the top board 40 is disposed on the casingbody 10 such that the lower flange portion 43 of the top board 40 ismounted on the mounting portion 101 formed at an peripheral edge of theupper opening 16 of the casing body 10. At this time, the upperprotrusions 144 formed in the top board 40 and the lower protrusions 131formed in the bottom wall 13 respectively abut the circularly arcuateturn-around portions 52 of the uppermost and bottommost heat absorbingpipes 50. Further, the side baffle plate 45 formed in the lower surfaceof the top board 40 on the other side wall 15 side is inserted into thespace formed between the ends of the circularly arcuate turn-aroundportions 52 on the other side wall 15 side and the inner surface of theother side wall 15. Furthermore, the upper baffle plate 46 formed in thelower surface of the top board 40 on the front wall 12 side is disposedso as to downward incline from the lower surface of the top board 40toward the entire upper edge of the opening of the combustion gas outletport 121.

Then, as shown in FIG. 9B, the fastening process is performed forbending the upper flange portion 102 of the casing body 10 against thelower flange portion 43 of the top board 40, whereby the upper opening16 of the casing body 10 is closed by the top board 40. With this, asubassembly in which the heat absorbing pipes 50, the inlet header 60,and the like are prefixed is assembled. As described above, in thepresent embodiment, the walls 11, 12, 13, 14, 15 of the casing body 10are integrally formed by drawing the single metal plate, and only theupper opening 16 of the casing body 10 with less affected by the drainis closed by the top board 40. Thus, it is possible to produce thecasing 2 having an excellent corrosion resistance without performingwelding or brazing but simply by connecting the casing body 10 and thetop board 40 by the fastening process.

Finally, the subassembly is placed in a heating furnace and a brazingprocess is performed. With this, members are fixed at portions to whichthe brazing materials are applied and the latent heat exchanger 1 isproduced. Since the casing body 10 and the heating absorbing pipes 50are subject to the heating (solution-annealed) during the brazingprocess, residual stresses in the casing body 10 generated by thedrawing process and the circularly arcuate turn-around portions 52 areremoved, so that even upon contacting with the strong acidic drain,stress-corrosion cracking can be prevented.

Next, one example of a water heater according to the present embodimentwill be described in detail.

FIG. 10 is a schematic block diagram showing the water heater accordingto the embodiment 1. A sensible heat exchanger 3 and the latent heatexchanger 1 are located in an apparatus body (not shown).

As shown in FIG. 10, the sensible heat exchanger 3 is arranged below thelatent heat exchanger 1. Also, a gas burner 4 for burning gas suppliedfrom a gas supply pipe is arranged below the sensible heat exchanger 3and further an air supply fan 5 for supplying combustion air is arrangedbelow the gas burner 4.

The sensible heat exchanger 3 comprises a number of fins 332 arranged inparallel and a meandering pipes 331 passing through the fins 332. Thesensible heat exchanger 3 and the latent heat exchanger 1 arepartitioned into upper and lower regions by the bottom wall 13 of thecasing body 10.

The sensible heat exchanger 3 communicates with the latent heatexchanger 1 via the combustion gas inlet port 111 described above. Thecombustion gas supplied into the latent heat exchanger 1 from thesensible heat exchanger 3 via the combustion gas inlet port 111 passesthrough the latent heat exchanger 1 and thereafter it is discharged outof the apparatus body from the combustion gas outlet port 121.

In the water heater of the present embodiment, the combustion gas isproduced by combustion of the gas burner 4 and the sensible heatexchanger 3 and the latent heat exchanger 1 are heated by the combustiongas. Then, sensible heat in the combustion gas is absorbed by thesensible heat exchanger 3 and latent heat in the combustion gas absorbedthe sensible heat is absorbed by the latent heat exchanger. At thistime, water vapor in the combustion gas is cooled below the dew pointtemperature, so that the strong acidic drain is generated and the draingenerated in the latent heat exchanger 1 drips on the bottom wall 13 ofthe casing body 10. As described above, however, the latent heatexchanger 1 of the present embodiment has the casing body 10 whose walls11, 12, 13, 14, 15 are integrally formed by the drawing, so that noconnection area by welding or brazing is formed in the lower area of thecasing 2. Therefore, the drain is not likely to be retained in the lowerarea of the casing 2, whereby it makes possible to discharge the drainsmoothly from the discharge opening 17 to the neutralizer. As a result,corrosion of the casing 2 due to the drain can be reduced, whereby thewater heater having high durability can be obtained.

The joint cylinder 68 of the inlet header 60 is connected to the watersupply pipe for introducing cold water from a water supply source suchas a water pipe and the joint cylinder 78 of the outlet header 70 isconnected to a connection pipe communicating to an upstream end of pipes331 of the sensible heat exchanger 3. Therefore, the cold water suppliedfrom the water supply pipe is heated to be hot water during passingthrough the latent heat exchanger 1 and the sensible heat exchanger 3and thereafter the hot water is supplied to a hot-water supplyingterminal such as a bathroom or a kitchen, from a hot-water supply pipeconnected to a downstream end of pipes 331 of the sensible heatexchanger 3.

Embodiment 2

Although in the above embodiment 1, a latent heat exchanger used for awater heater having a single heating circuit has been described, in thisembodiment 2, a latent heat exchanger used for a water heater having twoheating circuits will be described. The same elements as those of thelatent heat exchanger and the water heater in the embodiment 1 aredenoted by the same reference numerals, and a description thereof willbe are omitted.

FIG. 11 is a schematic perspective view from the back showing a latentheat exchanger according to the present embodiment 2.

As shown in FIG. 11, a casing of a latent heat exchanger 1 a has acasing body 10 and a top board 40 closing an upper opening of the casingbody 10, same as those of the latent heat exchanger 1 of theembodiment 1. However, an inside of the casing is partitioned by apartition wall W into a first region on the one side wall 14 side and asecond region on the other side wall 15 side, and first absorbing pipes50 a and second absorbing pipes 50 b are accommodated respectively inthe regions arranged in parallel along the left-right direction. Thestructures of the first and second heat absorbing pipes 50 a, 50 b aresame as those of embodiment 1.

As for the casing body 10, a back wall 11, a front wall 12, a bottomwall 13, one side wall 14, and the other side wall 15 are integrallyformed by drawing one single metal plate, same as that of theembodiment 1. Two combustion gas inlet ports 111 a, 111 b are formed inthe back wall 11 so as to introduce combustion gas into the first andsecond regions respectively. On the other hand, as shown in FIG. 12, onesingle combustion gas outlet port 121 communicating with the first andsecond regions is formed in the front wall 12. However, two combustiongas outlet ports may be formed in the front wall 12, same as the backwall 11. Furthermore, although not shown, first upstream end-insertingholes and first downstream end-inserting holes through which upstreamends and downstream ends of the first heat absorbing pipes 50 arespectively inserted are formed in the one side wall 14 and secondupstream end-inserting holes and second downstream end-inserting holesthrough which upstream ends and downstream ends of the second heatabsorbing pipes 50 b respectively inserted are formed in the other sidewall 15. Lower protrusions 131 abutting circularly arcuate turn-aroundportions of the first and second heat absorbing pipes 50 a, 50 b and adrain discharge opening 17 for discharging the drain are formed in thebottom wall 13.

Thus, in the latent heat exchanger 1 a of the present embodiment, thecasing body 10 does not have any connection areas by welding or brazing,so that there is no need of welding or brazing to assemble the casingbody 10. Also, since no connection area by welding or brazing is formedin the lower area of the casing, the drain is not likely to be retainedin the lower area when the drain is generated. Further, since the backwall 11, the front wall 12, the bottom wall 13, the one side wall 14,and the other side wall 15 are integrally formed by the drawing, thecasing can be easily formed with fewer members. Furthermore, since onlythe upper opening of the casing body 10 with less affected by the drainis closed by the top board 40, it is possible to produce the casinghaving an excellent corrosion resistance without performing welding orbrazing but simply by connecting the casing body 10 and the top board 40by the fastening process.

The top board 40 has the same configuration as that of the top board 40according to the embodiment 1, and the side baffle plate 45 is providedonly in the first region on the one side wall 14 side. Other side baffleplate may be provided also in the second region. However, in a casewhere the partition wall W is provided after accommodation of the secondheat absorbing pipes 50 b in the casing body 10, it is possible todispose the partition wall W near ends of the circularly arcuateturn-around portions of the second heat absorbing pipes 50 b. Thus, inthe present embodiment, the side baffle plate 45 can be provided ineither the first or the second region.

A first inlet header 60 a and a first outlet header 70 a which arerespectively connected to the upstream and downstream ends of the firstheat absorbing pipes 50 a are arranged outside the one side wall 14 anda second inlet header 60 b and a second outlet header 70 b which arerespectively connected to the upstream and downstream ends of the secondheat absorbing pipes 50 b are arranged outside the other side wall 15.Those headers respectively have a header main body and a header coversame as those of the embodiment 1.

FIG. 12 is a schematic block diagram showing one example of a waterheater having the latent heat exchanger 1 a described above.

In the water heater, combustion gas produced by a first gas burner 4 ais supplied, by an air supply fan 5 a, to a first sensible heatexchanger 3 a where sensible heat is recovered and further supplied tothe first region of the latent heat exchanger 1 a where latent heat isrecovered. Similarly, combustion gas produced by a second gas burner 4 bis supplied, by an air supply fan 5 a, to a second sensible heatexchanger 3 b where sensible heat is recovered and further supplied tothe second region of the latent heat exchanger 1 a where latent heat isrecovered. According to the water heater, for example, one heatingcircuit can be used for a hot water supply circuit and the other heatingcircuit can be used for a heating circuit.

Other Embodiments

(1) In the embodiments above, the top board is fastened to the casingbody by forming the upper flange in the casing body. Alternatively, acasing body may be fastened to a top board by forming an upper flange inthe top board.

(2) In the embodiments above, the side baffle plate is connected to thelower surface of the top board. Alternatively, a top board and a sidebaffle plate which are not connected to each other may be used, and theside baffle plate may be connected to a bottom wall before a casing bodyis connected to the top board after the accommodation of the heatabsorbing pipes. In this case, considering the noise described above, itis preferable that an upper end of the baffle plate are not extended toabut a lower surface of the top board.

As described in detail, the present invention is summarized as follows.

According to one aspect of the present invention, there is provided alatent heat exchanger comprising:

a casing having a flow path of combustion gas therein;

a heat absorbing pipe accommodated in the casing;

an inlet header for introducing fluid to be heated into the heatabsorbing pipe; and

an outlet header for discharging the fluid to be heated from the heatabsorbing pipe, wherein

the casing has a box-shaped casing body having an upper opening and atop board closing the upper opening of the casing body,

the casing body has a back wall, a front wall, a bottom wall having adrain discharging opening, one side wall having an upstreamend-inserting hole through which an upstream end of the heat absorbingpipe is inserted and a downstream end-inserting hole through which adownstream end of the heat absorbing pipe is inserted, and the otherside wall,

the back wall, the front wall, the bottom wall, the one side wall, andthe other side wall are integrally formed by drawing one single metalplate, and

the inlet header and the outlet header are respectively disposed outsidethe one side wall and connected to the upstream and downstream ends ofthe heat absorbing pipe led outside the one side wall through theupstream end-inserting hole and the downstream end-inserting hole.

According to the latent heat exchanger described above, since the backwall, the front wall, the bottom wall, the one side wall, and the otherside wall of the casing body are integrally formed by drawing the singlemetal plate, there is no need of welding or brazing to assemble thecasing body. Also, since no connection area by welding or brazing isformed in the lower area of the casing, generated drain is not likely tobe retained in the lower area of the casing. Therefore, it makespossible to smoothly discharge the drain from the drain dischargeopening formed in the lower area of the casing. Further, since thecasing body has the back wall, the front wall, the bottom wall, the oneside wall, and the other side wall, integrally formed by the drawing, itmakes possible to manufacture the latent heat exchanger easily withfewer members.

In the latent heat exchanger described above, the casing body and thetop board may be connected by the fastening process.

According to the latent heat exchanger described above, since the wallsof the casing body are integrally formed by drawing the single metalplate, in the assemble of the casing, only the upper opening of thecasing body with less affected by the drain is closed by the top board.Thus, it is possible to produce the casing having an excellent corrosionresistance simply by connecting the casing body and the top board by thefastening process.

Preferably, the latent heat exchanger described above has a heatabsorbing pipe in the casing having a piping structure in which astraight portion extending between the one side wall and the other sidewall and circularly arcuate turn-around portions located at the bothends on the one side wall side and the other side wall side are repeatedconsecutively. More preferably, the latent heat exchanger having thestructure described above further comprises a side baffle plate in aplate shape between the circularly arcuate turn-around portion on theother side wall side and an inner surface of the other side wall.

Since the heat absorbing pipe is arranged densely in the casing by useof the heat absorbing pipe having the above structure, the latent heatexchanger having a small size and higher heat efficiency can beobtained. Further, the casing body having the walls integrally formed bythe drawing is used in the latent heat exchanger, so that it isnecessary to lead out the upstream and downstream ends of the heatabsorbing pipe from the one side wall in connecting the heat absorbingpipe to the inlet header and the outlet header disposed outside the oneside wall. Thus, when the upstream and downstream ends of the heatabsorbing pipe are inserted through the upstream end-inserting hole andthe downstream end-inserting hole, respectively, there occurs a spacehaving a certain volume between the circularly arcuate turn-aroundportion on the other side wall side and an inner surface of the otherside wall. This causes the combustion gas introduced through thecombustion gas inlet port to flow in the space with less gas glowresistance, which may result in preventing the combustion gas fromefficiently contacting the heat absorbing pipe and reducing in heatefficiency. On the other hand, providing the side baffle plate in thespace between the circularly arcuate turn-around portion on the otherside wall side and the inner surface of the other side wall causes thecombustion gas to flow toward the heat absorbing pipe side, making iteasy for the combustion gas to contact the heat absorbing pipe, wherebyhigher heat efficiency can be obtained.

In the latent heat exchanger described above, when the back wall has acombustion gas inlet port for introducing the combustion gas into thecasing and the front wall has a gas combustion outlet port fordischarging the combustion gas out of the casing, respectively, the sidebaffle plate may have inclined faces inclined from ends on an inlet portside and an outlet port side toward a heat absorbing pipe side.

According to the latent heat exchanger described above, the flow path ofthe combustion gas is formed between the combustion gas inlet port inthe back wall and the combustion gas outlet port in the front wall. Theside baffle plate has the inclined faces inclined from the ends on theinlet port side and the outlet port side toward the heat absorbing pipeside, so that the combustion gas flows along the inclined faces.Therefore, according to the latent heat exchanger described above, itmakes easier for the combustion gas to contact the heat absorbing pipe,thereby allowing further enhancement of the heat efficiency.

Preferably, in the latent heat exchanger described above, the sidebaffle plate is formed such that an upper end is connected to a lowersurface of the top board and a lower end does not abut an inner surfaceof the bottom wall.

According to the latent heat exchanger described above, the casing inwhich the side baffle plate is positioned at a predetermined place canbe fabricated simply by closing the upper opening of the casing bodywith the top board to which the side baffle plate is connected. Further,if the side baffle plate extends to such an extent that the lower endthereof abuts the bottom wall, vibration of the side baffle plate istransmitted both to the top board and the bottom wall when thecombustion gas passes inside the casing, resulting in easy generation ofnoise. On the other hand, the side baffle plate is only connected to thelower surface of the top board but not the bottom wall, it makespossible to prevent such noise. Further, flow of drain is not disturbed,whereby it makes possible to discharge the drain smoothly. Moreover,since any connection portions are not formed between the bottom wall andthe side baffle plate, there is no need to take care of crevicecorrosion due to the drain.

According to a preferable aspect of the present invention whose objectis to fix a plurality of the heat absorbing pipes in the casing stably,the latent heat exchanger described above comprises,

a plurality of the heat absorbing pipes accommodated in the casing,wherein

the heat absorbing pipes each in the casing have a piping structure inwhich a straight portion extending between the one side wall and theother side wall and circularly arcuate turn-around portions are repeatedconsecutively,

the heat absorbing pipes are stacked at the flattened circularly arcuateturn-around portions between the top board and the bottom wall,

the circularly arcuate turn-around portions of the heat absorbing pipeseach have a cross section flattened in a direction that the heatabsorbing pipes are stacked one another, and

the top board and the bottom wall respectively have an upper protrusionand an lower protrusion, protruding inwardly into the casing, wherein

the upper protrusion abuts the uppermost circularly arcuate turn-aroundportions on a top board side and the lower protrusion abuts thebottommost circularly arcuate turn-around portions on a bottom wallside.

According to the latent heat exchanger described above, since thecircularly arcuate turn-around portions each of the heat absorbing pipesstacked between the top board and the bottom wall have a flattened crosssection, the heat absorbing pipes can be arranged more densely than theheat absorbing pipes having a circular cross section, whereby it makespossible to reduce a height in a direction that the heat absorbing pipesare stacked one another. Further, since the density of the arranged heatabsorbing pipes becomes higher, an amount of ineffective combustion gaswhich is discharged out of the casing without contact relative to theheat absorbing pipes becomes less, whereby higher thermal efficiency canbe obtained. On the other hand, in a case where the heat absorbing pipesare stacked between the top board and the bottom wall, vibration anddeformation of the heat absorbing pipes are likely to be occurred.However, according to the latent heat exchanger above, the top board andthe bottom wall respectively have the upper and lower protrusions whichprotrude inwardly into the casing and those upper and lower protrusionsabut the flattened circularly arcuate turn-around portions of the heatabsorbing pipes, so that the heat absorbing pipes can be fixed stablywithout using other fixing member. Moreover, since the casing can beproduced by closing the upper opening of the casing body integrallyformed by the back wall, the front wall, the one side wall, and theother side wall, with the top board, the heat absorbing pipes can befixed upon closing the upper opening with the top board, without usingother fixing member. Therefore, high productivity can be obtained.

Preferably, in the latent heat exchanger having the plurality of theheat absorbing pipes,

the heat absorbing pipes each in the casing have a piping structure inwhich a straight portion extending between the one side wall and theother side wall and the circularly arcuate turn-around portions locatedat both ends on the one side wall side and the other side wall side arerepeated consecutively,

the top board has upper protrusions located at the both ends on the oneside wall side and the other side wall side,

the upper protrusions at the both ends respectively abut the uppermostcircularly arcuate turn-around portions located at the both ends,

the bottom wall has lower protrusions located at the both ends on theone side wall side and the other side wall side, and

the lower protrusions at the both ends respectively abut the bottommostcircularly arcuate turn-around portions located at the both ends.

According to the latent heat exchanger described above, the flattenedcircularly arcuate turn-around portions of the heat absorbing pipes areformed at the both ends on the one and other side wall sides and theupper and lower protrusions formed in the top board and the bottom wallrespectively abut the uppermost and bottommost circularly arcuateturn-around portions at the both ends, so that the heat absorbing pipescan be fixed more stably in the casing.

According to another preferable aspect of the present invention whoseobject is to prevent water leak from the header, in the latent heatexchanger described above,

at least one of the inlet header and the outlet header has a header mainbody in a dish shape and a header cover in a dish shape to be internallyfitted to the header main body,

the header main body and the header cover are connected by brazing suchthat openings face each other,

the header main body has a main body bottom plate having connectionholes to be connected to the upstream ends or the downstream ends of theheat absorbing pipes and a main body peripheral wall extended from aperipheral end of the main body bottom plate toward a header cover sideand opened toward the header cover side,

the header cover has a cover bottom plate having an inflow port or anoutflow port and a cover peripheral wall extended from a peripheral endof the cover bottom plate toward a header main body side and openedtoward the header main body side, and

the header main body and the header cover are formed such that an outersurface of the cover peripheral wall fits into an inner surface of themain body peripheral wall and a brazing reservoir is formed between theinner surface of the main body peripheral wall and the outer surface ofthe cover peripheral wall, in a state where the header main body and theheader cover are fitted to each other.

In a conventional way of connecting a header main body and a headercover, the brazing material has been applied only on edge face of themain body open end of the main body peripheral wall, so that scatteringand dripping of the brazing material easily occur, whereby the headermain body and the header cover are difficult to connect to each otherreliably. On the other hand, according to the latent heat exchangerdescribed above, the brazing reservoir is formed between the innersurface of the main body peripheral wall and the outer surface of thecover peripheral wall, in a state where the header main body and theheader cover are fitted to each other in order to connect the headermain boy in a dish shape to the header cover in a dish shape by brazing.Accordingly, not only scattering and dripping of the brazing materialcan be prevented in a brazing process, but also a connection areabetween the inner surface of the main body peripheral wall and the outersurface of a cover peripheral wall can be enlarge, as compared to a casewhere the brazing material is applied only on the edge face of the mainbody open end as the conventional method.

In the latent heat exchanger having the header including the structuredescribed above,

the main body peripheral wall may be formed such that the main body openend is widen outwardly.

According to the latent heat exchanger described above, it makespossible to enlarge the connection area between the inner surface of themain body peripheral wall and the outer surface of the cover peripheralwall easily.

In the latent heat exchanger having the header including the structuredescribed above,

at least a part of the main body open end of the main body peripheralwall may be extended higher than an outer peripheral surface of thecover bottom plate in a cross-sectional direction, in a state where theheader main body and the header cover are fitted to each other.

According to the latent heat exchanger described above, it makespossible to further enlarge the connection area between the innersurface of the main body peripheral wall and the outer surface of thecover peripheral wall.

In the latent heat exchanger having the header including the structuredescribed above,

a claw, which is bent toward the header cover side after the header mainbody and the header cover are fitted to each other, may be formed in themain body open end of the main body peripheral wall.

When the header main body and the header cover are brazed to each other,the header cover is pressed into the header main body firstly. However,due to fabrication errors of both peripheral walls of those members, theheader cover may be shifted with respect to the header main body afterpressing-in. As a result, the header main body is not connected to theheader cover precisely. On the other hand, the claw to be bent towardthe header cover side is provided on the main body open end of the mainbody peripheral wall, such a shift of the header cover can be preventedby bending the claw after the header cover is pressed into the headermain body.

Preferably, in the latent heat exchanger having the header including thestructure described above,

the main body peripheral wall is formed into substantially a rectangularshape having a pair of long sides and a pair of short sides, and

the claw is formed in at least one of the main body open end of the pairof the long sides.

More preferably, claws are respectively formed in the main body open endof the pair of the opposing long sides of the main body peripheral wall,and

the claws of the main body peripheral wall formed in the long sides arerespectively arranged such that they are not overlapped in a short sidedirection.

According to the latent heat exchanger described above, the shift of theheader cover upon fitting the header cover to the header main body canbe reliably prevented.

According to yet another preferable aspect of the present inventionwhose object is to manufacture a water heater having a plurality ofheating circuits,

the latent heat exchanger described above further comprising:

a second heat absorbing pipe accommodated in the casing and arranged inparallel with the heat absorbing pipe;

a second inlet header for introducing second fluid to be heated into thesecond heat absorbing pipe;

a second outlet header for discharging the second fluid to be heatedfrom the second heat absorbing pipe, wherein

the other side wall has a second upstream end-inserting hole throughwhich an upstream end of the second heat absorbing pipe is inserted anda second downstream end-inserting hole through which a downstream end ofthe second heat absorbing pipe is inserted, and

the second inlet header and the second outlet header are respectivelydisposed outside the other side wall and connected to the upstream anddownstream ends of the second heat absorbing pipe led outside the otherside wall through the second upstream end-inserting hole and the seconddownstream end-inserting hole.

According to the latent heat exchanger described above, in the latentheat exchanger used for a water heater having the plurality of theheating circuits, not only corrosion due to the drain can be prevented,but also the latent heat exchanger can be manufactured easily.

Further, according to the present invention, a water heater having thelatent heat exchanger described above can be provided.

The present application claims priorities under the Paris Convention onJapanese patent applications No. 2010-290153, No. 2010-290154, and No.2010-290155, all of which are filed on Dec. 27, 2010, and entirecontents of which are incorporated herein by reference.

INDUSTRIAL APPLICABILITY

According to the present invention, there can be provided a latent heatexchanger and water heater using thereof which are excellent indurability and easy manufactured.

1. A latent heat exchanger comprising: a casing having a flow path ofcombustion gas therein; a heat absorbing pipe accommodated in thecasing; an inlet header for introducing fluid to be heated into the heatabsorbing pipe; and an outlet header for discharging the fluid to beheated from the heat absorbing pipe, wherein the casing has a box-shapedcasing body having an upper opening and a top board closing the upperopening of the casing body, the casing body has a back wall, a frontwall, a bottom wall having a drain discharging opening, one side wallhaving an upstream end-inserting hole through which an upstream end ofthe heat absorbing pipe is inserted and a downstream end-inserting holethrough which a downstream end of the heat absorbing pipe is inserted,and the other side wall, the back wall, the front wall, the bottom wall,the one side wall, and the other side wall are integrally formed bydrawing one single metal plate, and the inlet header and the outletheader are respectively disposed outside the one side wall and connectedto the upstream and downstream ends of the heat absorbing pipe ledoutside the one side wall through the upstream end-inserting hole andthe downstream end-inserting hole.
 2. The latent heat exchangeraccording to claim 1, wherein the casing body and the top board areconnected by a fastening process.
 3. The latent heat exchanger accordingto claim 1, wherein the heat absorbing pipe in the casing has a pipingstructure in which a straight portion extending between the one sidewall and the other side wall and circularly arcuate turn-around portionslocated at both ends on one side wall side and the other side wall sideare repeated consecutively.
 4. The latent heat exchanger according toclaim 3, further comprising a side baffle plate in a plate shape betweenthe circularly arcuate turn-around portion located on the other sidewall side and an inner surface of the other side wall.
 5. The latentheat exchanger according to claim 4, wherein the back wall has acombustion gas inlet port for introducing the combustion gas into thecasing, the front wall has a combustion gas outlet port for dischargingthe combustion gas out of the casing, and the side baffle plate hasinclined faces inclined from ends on an inlet port side and an outletport side toward a heat absorbing pipe side.
 6. The latent heatexchanger according to claim 4, wherein an upper end of the side baffleplate is connected to a lower surface of the top board, and a lower endof the side baffle plate does not abut an inner surface of the bottomwall.
 7. A water heater having the latent heat exchanger according toclaim
 1. 8. The latent heat exchanger according to claim 1, wherein thetop board and the bottom wall respectively have an upper protrusion andan lower protrusion, protruding inwardly into the casing, and the upperprotrusion abuts the uppermost circularly arcuate turn-around portion ona top board side and the lower protrusion abuts the bottommostcircularly arcuate turn-around portion on a bottom wall side.
 9. Thelatent heat exchanger according to claim 5, further comprising an upperbaffle plate inclined downward from a lower surface of the top board ona front wall side toward an upper edge of an opening of the gas outletport.
 10. The latent heat exchanger according to claim 3, wherein aplurality of the heat absorbing pipes are accommodated in the casing,wherein the circularly arcuate turn-around portions of the heatabsorbing pipes each have a cross section flattened in a direction thatthe heat absorbing pipes are stacked one another, and the heat absorbingpipes are stacked at the flattened circularly arcuate turn-aroundportions between the top board and the bottom wall.
 11. A method ofmanufacturing the latent heat exchanger according to claim 1, comprisingthe steps of: inserting the upstream and downstream ends of the heatabsorbing pipe through the upstream end-inserting hole and thedownstream end-inserting hole of the one side wall respectively; leadingthe upstream and downstream ends of the heat absorbing pipe outside theone side wall; applying a brazing material to boundaries between outersurfaces of the led-out heat absorbing pipe and the upstreamends-inserting hole and the downstream ends-inserting hole; insertingthe upstream and the downstream ends of the led-out heat absorbing pipethrough connection holes of header main bodies of the inlet and outletheaders respectively: applying a brazing material to boundaries betweenouter surfaces of the upstream and downstream ends of the heat absorbingpipe and the connection holes; closing openings of the header mainbodies with header covers respectively; applying a brazing material toboundaries between inner surfaces of main body peripheral walls of theheader main bodies and outer surfaces of cover peripheral walls of theheader covers; closing the upper opening of the casing body with the topboard to form a subassembly in which the casing body, the top board, theheat absorbing pipe, the inlet header, and the outlet header areintegrally formed; and heating the subassembly in a heating furnace.